Nuclear magnetic resonance flow methods have been developed to measure blood flow in perepheral vessels using magnetic markers for venous flow or self tag methods for pulsatile flow. Specific vessels are tuned in by a "ranging" method whereby a sensitive region is localized by the interaction of external magnetic fields. Several NMR signal enhancement systems are being investigated to increase the sensitivity of the method based on observations of double resonance phenomena whereby short relaxation time materials i.e., rubber surrounding the proton signal sample, couple with the flow proton signal to improve the S/N ratio. Similar systems utilizing NMR coupled to electron spin resonance are also being investigated. Flow signals from specific blood vessels within the brain have been localized by a "ranging" method and detected by the self tag method. Detection systems at high, low, and weak fields have been set up to study the time limits of detectability of proton magnetic markers in blood.